The invention relates to a method for continuously manufacturing a composite tube comprising a metal part and at least an inner part made of plastics material.
Methods of this type are already known, for example by U.S. Pat. No. 3,376,181 to the Continental Can Company (U.S. Ser. No. 298,854), in which a metal tube is made from a strip material closed on itself and longitudinally seamed; directly after seaming, a layer of plastics material is injected into the tube obtained, which constitutes an inner layer lining the metal surface. According to this same patent, to facilitate adherence of the plastics material to the metal, a vacuum is created between the metal tube and the plastics material downstream of a nozzle which furnishes this material in the form of a cone which widens and finishes by being applied on the inner surface of the metal. As a variant, it is also possible to exert, instead of the vacuum, an excess pressure in the part of the composite tube located downstream of the nozzle.
The metal tube lined with plastics material as described in the above-mentioned patent is intended to be cut into discrete lengths to constitute the body of cans which are thereafter closed by a bottom and a lid. It is important that the plastics material adheres well to the metal, but it must be admitted that the cans thus manufactured are not subjected, during use, to stresses putting this adherence to the test.
It is a principal object of the invention to provide a composite tube comprising a metal part and at least an inner part of plastics material, preferably with an outer part likewise of plastics material, which may be used in plumbing for the supply and/or evacuation of various domestic appliances such as wash-basins, bath-tubs, showers, sinks, etc. A tube of this type must withstand treatments which impose severe stresses on the adherence between the metal and the plastics material. For example, on hot water circuits, the composite tube must withstand numerous successive cycles of heating and cooling between ambient temperature and 100.degree. C., without any risk of separation of the metal and the plastics material.
Copper or lead tubes have heretofore been currently used. These two metals have their qualities and their shortcomings. Annealed copper bends and curves easily, but it is then difficult to straighten it perfectly. Lead is very malleable; it bends and straightens up fairly easily, but it is not sufficiently rigid compared with copper and, moreover, it is deformed by creeping even at ambient temperature.
It is an object of the invention to provide a composite tube which is completely inert with respect to water, due to an inner layer of plastics material, and which combines the advantages of copper and lead without having the drawbacks thereof. In brief, the invention aims at obtaining a composite tube which is as malleable as lead and as rigid as copper, so that it may easily be bent and straightened up and so that it keeps its shape even at a continuous temperature of 80.degree. C.
It is certain that this involves excellent adherence between the metal and the plastics material, to a degree which is not necessary with the composite tube of the above-mentioned patent and which this composite tube does not present.